Upgrade architecture + 5.0 Bot API (#469)

Upgrade architecture + 5.0 Bot API (#469)
* Moved `methods`, `types` and `client` to root package
* Removed update handler from routers to dispatcher
* Reworked events propagation mechanism to handlers
* Reworked inner middlewares logic (very small change)
* Updated to Bot API 5.0
* Initial migration from MkDocs to Sphinx + config for readthedocs

docs2/api/session/aiohttp.rst

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+#######
+aiohttp
+#######
+
+AiohttpSession represents a wrapper-class around `ClientSession` from `aiohttp <https://pypi.org/project/aiohttp/>`_
+
+Currently `AiohttpSession` is a default session used in `aiogram.Bot`
+
+.. autoclass:: aiogram.client.session.aiohttp.AiohttpSession
+
+Usage example
+=============
+
+.. code-block::
+
+    from aiogram import Bot
+    from aiogram.session.aiohttp import AiohttpSession
+
+    session = AiohttpSession()
+    Bot('42:token', session=session)
+
+
+Proxy requests in AiohttpSession
+================================
+
+In order to use AiohttpSession with proxy connector you have to install `aiohttp-socks <https://pypi.org/project/aiohttp-socks>`_
+
+Binding session to bot:
+
+.. code-block::
+
+    from aiogram import Bot
+    from aiogram.client.session.aiohttp import AiohttpSession
+
+    session = AiohttpSession(proxy="protocol://host:port/")
+    Bot(token="bot token", session=session)
+
+
+.. note::
+
+    Only following protocols are supported: http(tunneling), socks4(a), socks5
+    as aiohttp_socks `documentation <https://github.com/romis2012/aiohttp-socks/blob/master/README.md>`_ claims.
+
+
+Authorization
+-------------
+
+Proxy authorization credentials can be specified in proxy URL or come as an instance of :obj:`aiohttp.BasicAuth` containing
+login and password.
+
+Consider examples:
+
+.. code-block::
+
+    from aiohttp import BasicAuth
+    from aiogram.client.session.aiohttp import AiohttpSession
+
+    auth = BasicAuth(login="user", password="password")
+    session = AiohttpSession(proxy=("protocol://host:port", auth))
+
+
+or simply include your basic auth credential in URL
+
+.. code-block::
+
+    session = AiohttpSession(proxy="protocol://user:password@host:port")
+
+
+.. note::
+
+    Aiogram prefers `BasicAuth` over username and password in URL, so
+    if proxy URL contains login and password and `BasicAuth` object is passed at the same time
+    aiogram will use login and password from `BasicAuth` instance.
+
+
+Proxy chains
+------------
+
+Since `aiohttp-socks <https://pypi.org/project/aiohttp-socks/>`_ supports proxy chains, you're able to use them in aiogram
+
+Example of chain proxies:
+
+.. code-block::
+
+    from aiohttp import BasicAuth
+    from aiogram.client.session.aiohttp import AiohttpSession
+
+    auth = BasicAuth(login="user", password="password")
+    session = AiohttpSession(
+        proxy={
+            "protocol0://host0:port0",
+            "protocol1://user:password@host1:port1",
+            ("protocol2://host2:port2", auth),
+        }  # can be any iterable if not set
+    )

docs2/api/session/base.rst

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+####
+Base
+####
+
+Abstract session for all client sessions
+
+.. autoclass:: aiogram.client.session.base.BaseSession
+    :members:

docs2/api/session/custom_server.rst

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+Use Custom API server
+=====================
+
+.. autoclass:: aiogram.client.telegram.TelegramAPIServer
+    :members:
+
+For example, if you want to use self-hosted API server:
+
+.. code-block:: python3
+
+    session = AiohttpSession()
+    session.api = TelegramAPIServer.from_base('http://localhost:8082')
+    bot = Bot(..., session=session)

docs2/api/session/index.rst

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+##############
+Client session
+##############
+
+Client sessions is used for interacting with API server.
+
+.. toctree::
+    custom_server
+    base
+    aiohttp